The thermolysis at about 100 Deg of Na[C8H14B(Et)OH] (2), prepd. from 9-Et-9-BBN (1) and NaOH, leads in the presence of NaHBEt3 as catalyst to ethane and the solid NaOBC8H14 (3), which crystallizes with one mole THF as the tetrameric heterocubane 4 in the triclinic space group P.hivin.1. As detd. by x-ray crystallog., 4 contains a slightly distorted central Na4O4 cube with C8H14B and THF substituents at the oxygen and the sodium atoms resp. 3 Can also be prepd. by heating an equimolar mixt. of Na[H2BC8H14] (5) and Na[(HO)2BC8H14] (6), or from (9H-9-BBN)2 and NaOH and from 9-HO-9-BBN and NaH in THF.